I'm probably the only person on Earth who did this, but I used polymer over-bake clay for a pot. I left it outside for a full year in the sun and weather, and it looked like it didn't weather at all. This spring, I put a small tree in it as a test and also to mess around with rocks and moss.
The pot is still perfectly good as far as I can tell. The funny thing is it's slight bendy, so I don't think I could break it without trying hard to do so. I have another one I made last winter that has no trees yet. It's much thinner and flatter, so who knows if that will work.
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